Conventional artificial nipples, which are attached to a bottle that holds milk or breast milk collected beforehand, are widely used.
In particular, an infant suctions milk that is held in a nursing container through sucking on an artificial nipple, upon lactation out of a nursing container. As a result, the milk volume decreases, and the pressure in the bottle drops proportionally. Milk becomes thus harder to suction, and negative pressure causes the artificial nipple to collapse.
Therefore, some instances of artificial nipples are found (Patent Literature 1, FIG. 2; Patent Literature 2, FIG. 2) in which downwardly-protruding valve bodies are provided at a flange section of a base section at the lower end of the artificial nipple, so that the valve bodies form a check valve that leads external air into the bottle.